Abstract
Escherichia coli sequence type ST131 (from phylogenetic group B2), often carrying the extended-spectrum-β-lactamase (ESBL) gene bla CTX-M-15, is an emerging globally disseminated pathogen that has received comparatively little attention in the United States. Accordingly, a convenience sample of 351 ESBL-producing E. coli isolates from 15 U.S. centers (collected in 2000 to 2009) underwent PCR-based phylotyping and detection of ST131 and bla CTX-M-15. A total of 200 isolates, comprising 4 groups of 50 isolates each that were (i) bla CTX-M-15 negative non-ST131, (ii) bla CTX-M-15 positive non-ST131, (iii) bla CTX-M-15 negative ST131, or (iv) bla CTX-M-15 positive ST131, also underwent virulence genotyping, antimicrobial susceptibility testing, and pulsed-field gel electrophoresis (PFGE). Overall, 201 (57%) isolates exhibited bla CTX-M-15, whereas 165 (47%) were ST131. ST131 accounted for 56% of bla CTX-M-15-positive-versus 35% of bla CTX-M-15-negative isolates (PCTX-M-15 status, with groups A (bla CTX-M-15-positive isolates) andD(bla CTX-M-15- negative isolates) predominating. Both bla CTX-M-15 and ST131 occurred at all participating centers, were recovered from children and adults, increased significantly in prevalence post-2003, and were associated with molecularly inferred virulence. Compared with non- ST131 isolates, ST131 isolates had higher virulence scores, distinctive virulence profiles, and more-homogeneous PFGE profiles. bla CTX-M-15 was associated with extensive antimicrobial resistance and ST131 with fluoroquinolone resistance. Thus, E. coli ST131 and bla CTX-M-15 are emergent, widely distributed, and predominant among ESBL-positive E. coli strains in the United States, among children and adults alike. Enhanced virulence and antimicrobial resistance have likely promoted the epidemiological success of these emerging public health threats.